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Quinones addition reactions

See also Ling, X, Poupon, E., Rueden, E. J., and Theodorakis E. A., Unified synthesis of quinone sesquiterpenes based on a radical decarboxylation and quinone addition reaction, /. Am. Chem. Soc., 124, 2002. [Pg.1353]

As the quinone stabilizer is consumed, the peroxy radicals initiate the addition chain propagation reactions through the formation of styryl radicals. In dilute solutions, the reaction between styrene and fumarate ester foUows an alternating sequence. However, in concentrated resin solutions, the alternating addition reaction is impeded at the onset of the physical gel. The Hquid resin forms an intractable gel when only 2% of the fumarate unsaturation is cross-linked with styrene. The gel is initiated through small micelles (12) that form the nuclei for the expansion of the cross-linked network. [Pg.317]

Quinone Methides. The reaction between aldehydes and alkylphenols can also be base-cataly2ed. Under mild conditions, 2,6-DTBP reacts with formaldehyde in the presence of a base to produce the methylol derivative (22) which reacts further with base to eliminate a molecule of water and form a reactive intermediate, the quinone methide (23). Quinone methides undergo a broad array of transformations by way of addition reactions. These molecules ate conjugated homologues of vinyl ketones, but are more reactive because of the driving force associated with rearomatization after addition. An example of this type of addition is between the quinone methide and methanol to produce the substituted ben2yl methyl ether (24). [Pg.61]

Rifamycin S also undergoes conjugate addition reactions to the quinone ring by a variety of nucleophiles including ammonia, primary and secondary amines, mercaptans, carbanions, and enamines giving the C-3 substituted derivatives (38) of rifamycin SV (117,120,121). Many of the derivatives show excellent antibacterial properties (109,118,122,123). The 3-cycHc amino derivatives of rifamycin SV also inhibit the polymerase of RNA tumor vimses (123,124). [Pg.498]

Addition Reactions. The addition of nucleophiles to quinones is often an acid-catalyzed, Michael-type reductive process (7,43,44). The addition of benzenethiol to 1,4-benzoquinone (2) was studied by A. Michael for a better understanding of valence in organic chemistry (45). The presence of the reduced product thiophenyUiydroquinone (52), the cross-oxidation product 2-thiophenyl-1,4-benzoquinone [18232-03-6] (53), and multiple-addition products such as 2,5-(bis(thiophenyl)-l,4-benzoquinone [17058-53-6] (54) and 2,6-bis(thiophenyl)-l,4-benzoquinone [121194-11-4] (55), is typical ofmany such transformations. [Pg.409]

SCHEME 2.16 Additional reaction pathway for the generation of the quinone methide in the gas phase oxidation of 2-methylphenyl radical, investigated by the hybrid functional MPW1K (reproduced from Ref. [23] with permission from American Chemical Society). [Pg.58]

Ralph, J. Young, R. A. Stereochemical aspects of addition reactions involving lignin model quinone methides. J. Wood Chem. Technol. 1983, 3, 161-181. [Pg.415]

Hemmingson, J. A. Leary, G. The chemistry of reactive lignin intermediates. Part II. Addition reactions of vinyl-substituted quinone methides in aqueous solution. J. Chem. Soc., Perkin Trans. 1975, 2, 1584-1587. [Pg.417]

The mercaptol alcohol rac-14 undergoes facile Michael addition reaction with quinone ketal 13 which is commercially available or can be readily prepared. [Pg.149]

These compounds have been prepared via oxidative addition reactions between the appropriate phosphate or phosphine and either a quinone or via displacement reactions with a suitable diol. Compounds 81 and 83 were prepared by such a displacement reaction between monocyclic pentaoxyphosphorane 317 and 3-fluorocatechol or catechol in toluene, respectively. This reaction takes advantage of the chelation effect of forming a bicyclic system from a monocyclic one <1997IC5730>. Compound 82 and compound 84 were synthesized via oxidation addition between tetrachloroquinone and the respective sulfur-containing cyclic phosphate or phosphine <1997IC5730>. Compound 93 was prepared from the phosphine 318 and the diol 319 in the presence of iV-chlorodiisopropylamine in an ether solution <1998IC93>. [Pg.565]

Addition reactions, 20 243. See also Electrophilic addition reactions aldehydes, 2 63-64 allyl alcohol, 2 234-239 butadiene, 4 368—370 carboxylic acids, 5 44-45 ethylene, 10 597—598 quinoline, 21 184 quinone, 21 246-261 toluene, 25 165... [Pg.15]

Combination of an Ri, radical with an Ra radical yields the single p-qninone methide dimer (V). Here the quinone methide cannot become stabilized by an intramolecnlar addition reaction. Instead, nucleophilic attack of its y-carbon atom occurs by a hydroxyl ion from the medium, for example aromatization and protonation of the phenoxido ion thus formed give rise to guaiacylglycerol- 3-coniferyl ether (VI), again in racemic form dc-spite its two asymmetric carbon atoms. Since attack by the extraneous hydroxyl ion can occur on either side of C-y of the p-quinone methide (V), complete equilibration of the specific hydrogens from the original conifcryl alcohol moiety in the lower half of (V) presumably occurs (sec formulae on p. 131). [Pg.126]

Diazomethane is capable of addition reactions with double bonds. Pyrazoline rings are formed. Studebaker et al. (38) saw in this reaction an indication of quinone groups ... [Pg.192]

Similar waves in the cathodic polarogram were observed by Donnet and Henrich 58) using oxidized carbon black. The wave disappeared after treatment with isobutyronitrile. It was assumed that isobutyro-nitrile gives an addition reaction with quinones. No reaction with this reagent was observed after reduction with hydrogen iodide, after treatment with aniline, or after treatment with diazomethane. The latter finding confirms the assumption by Studebaker et al. 38) that diazomethane is added to the quinones in the carbon black surface. [Pg.204]

A range of addition reactions of (TMS)3GeH with alkynes, alkenes, ketones, azines, and quinones has been studied using EPR. In addition, synthetic studies of hydrogermylation of alkynes have shown that the reaction proceeds regio- and stereo-selectively, whereas reactions with alkenes do not take place (presumably owing to the reversibility of the germyl radical addition) (Scheme 29). [Pg.137]

Phenol-induced oxidative stress mediated by thiol oxidation, antioxidant depletion, and enhanced free radical production plays a key role in the deleterious activities of certain phenols. In this mode of DNA damage, the phenol does not interact with DNA directly and the observed genotoxicity is caused by an indirect mechanism of action induced by ROS. A direct mode of phenol-induced genotoxicity involves covalent DNA adduction derived from electrophilic species of phenols produced by metabolic activation. Oxidative metabolism of phenols can generate quinone intermediates that react covalently with N-1,N of dG to form benzetheno-type adducts. Our laboratory has also recently shown that phenoxyl radicals can participate in direct radical addition reactions with C-8 of dG to form oxygen (O)-adducts. Because the metabolism of phenols can also generate C-adducts at C-8 of dG, a case can be made that phenoxyl radicals display ambident (O vs. C) electrophilicity in DNA adduction. [Pg.208]

Depending on the oxidation conditions, benzene and its substituted derivatives, and polycyclic aromatic hydrocarbons may be converted to phenols and quinones. Alkoxylation and acyloxylation are also possible. Addition reactions may afford dihydrodiols, epoxides, and endoperoxides. [Pg.491]

Routes to benzo-fused derivatives of 1,4-dioxanes, 1,4-oxathianes and 1,4-dithianes make use of anions or dianions of the appropriate 1,2-disubstituted benzene. An alternative approach to the synthesis of 1,4-benzodioxanes involves Diels-Alder addition reactions of alkenes across the quinone function of 1,2-benzoquinones, e.g. (352) — (353). [Pg.640]

PQQ and the other quinone prosthetic groups described here all function in reactions that would be possible for pyridine nucleotide or flavin coenzymes. All of them, like the flavins, can exist in oxidized, half-reduced semiquinone and fully reduced dihydro forms. The questions to be asked are the same as we asked for flavins. How do the substrates react How is the reduced cofactor reoxidized In nonenzymatic reactions alcohols, amines, and enolate anions all add at C-5 of PQQ to give adducts such as that shown for methanol in Eq. 15-51, step a 444,449,449a Although many additional reactions are possible, this addition is a reasonable first step in the mechanism shown in Eq. 15-51. An enzymatic base could remove a proton as is indicated in step b to give PQQH2. The pathway for reoxidation (step c) might involve a cytochrome b, cytochrome c, or bound ubiquinone.445 446... [Pg.815]

The imine bond of 4H- and 6H- 1,3-oxazines enters into addition reactions with quinones and alcohols. Thus, for example, the triphenyl derivative (50) forms a 1 1 adduct with 1,4-benzoquinone (69LA(723)lll) and the oxazin-6-ones (51), when heated in methanol, give 2-methoxy-2,3-dihydro derivatives (Scheme 15) (72CJC584). [Pg.1003]

These compounds offer interesting possibilities for further elaboration as they enter into addition reactions with, for example, the 1,2-quinone (60), yielding tricyclic compounds (61) (79TL237), and their bicyclic analogues (62) combine with phenyl isocyanate to give adducts (63), which eliminate carbon dioxide to afford pyrimidine betaines (64). Similarly, dialkyl acetylenedicarboxylates produce quinolizinones (65) (Scheme 19) (79CB1585). [Pg.1004]

Photoinitiation of polymerization can be obtained through a variety of photochemical reactions which produce reactive free radicals. These radicals then lead to the formation of the polymer chains through the addition of further monomer units to the end of a chain in a sequence of radical addition reactions (Figure 6.10). A photoinitiator of polymerization is therefore a molecule which produces free radicals under the action of light. Benzo-phenone and other aromatic ketones can be used as photoinitiators, since a pair of free radicals is formed in the hydrogen abstraction reaction. Some quinones behave similarly, for example anthraquinone in the presence of hydrogen donor substrates such as tetrahydrofuran. [Pg.197]

Besides alkenes and alkynes, other multiple bonds can be used as acceptors in addition reactions of carbon radicals provided the usual requirements of reactivity and selectivity are met. Other types of carbon-carbon multiple bonds that have been used as acceptors include dienes,162 allenes,61 enolates (and ni-tronates, see below) and quinones.223 Even highly strained cr-bonds have served as acceptors on occasion.224... [Pg.765]

Quinones are also strong oxidants, and their potential as radiation sensitizers has been investigated on the model level. Again, ET competes with addition (Simic and Hayon 1972, 1973 Hayon and Simic 1973). With carbon-centered radicals, a C-C bond is formed in the addition reaction, and subsequent reactions are different (von Sonntag et al. 2004) from the adducts formed with nitro compounds. [Pg.302]

These questions were addressed in studies of the reactions ofp-1 and / -Me-1 + in aqueous solution. The quinone methide p-1 was generated by photoheterolysis of neutral 4-hydroxybenzyl acetate in water, and ks = 3.3 s 1 determined for addition of water.52 The O-methylated quinone methide / -Me-l+ was generated as an intermediate of solvolysis of neutral precursors in water,128 and ks = 2.5 x 108 s 1 for addition of water was determined by using the diffusion-limited rate of nucleophile addition of azide anion to / -Me-l+ as a clock for the slower addition reaction of solvent.135,138 These data show that methylation ofp-1 causes an enormous 6 x 107-fold increase in the reactivity of the electrophile with solvent water.52... [Pg.70]

Nucleophile addition to a quinone methide is formally a Michael addition reaction.153 However, an important difference between 1,6-addition of nucleophiles to / -quinone methides and conventional Michael addition reactions is the aromatization of the cyclohexadiene ring that accompanies this addition. The effect of aromatic ring formation on the thermodynamic driving force for 1,6-addition of water to p-1 has been evaluated by comparing the thermodynamics... [Pg.76]

Fig. 4 (A) Free energy reaction profile for the reversible addition of Br to the di-Q -CF3-substituted quinone methide 48, constructed using rate and equilibrium data from Ref.91 (B) Free energy reaction profile for the reversible addition of Br to the simple quinone methide p-1, constructed using rate and equilibrium data from Ref.52 These nucleophile addition reactions show similar thermodynamic driving force, but both the formation and reaction of 48 are slow because of the large intrinsic barrier A for nucleophile addition. Fig. 4 (A) Free energy reaction profile for the reversible addition of Br to the di-Q -CF3-substituted quinone methide 48, constructed using rate and equilibrium data from Ref.91 (B) Free energy reaction profile for the reversible addition of Br to the simple quinone methide p-1, constructed using rate and equilibrium data from Ref.52 These nucleophile addition reactions show similar thermodynamic driving force, but both the formation and reaction of 48 are slow because of the large intrinsic barrier A for nucleophile addition.

See other pages where Quinones addition reactions is mentioned: [Pg.412]    [Pg.1325]    [Pg.412]    [Pg.1325]    [Pg.254]    [Pg.1096]    [Pg.220]    [Pg.391]    [Pg.70]    [Pg.155]    [Pg.57]    [Pg.82]    [Pg.741]    [Pg.1434]    [Pg.989]    [Pg.1311]    [Pg.1311]    [Pg.360]    [Pg.68]    [Pg.44]    [Pg.82]   
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See also in sourсe #XX -- [ Pg.410 ]

See also in sourсe #XX -- [ Pg.410 ]

See also in sourсe #XX -- [ Pg.97 , Pg.410 ]




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Quinones reaction

Reaction LXXXIV.—Addition of Phenols to Quinones

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